The purpose of this research is to continue to analyze sensory mechanisms in dental tissue. Since teeth primarily sense pain, these studies will improve our understanding of basic pain mechanisms. Comparisons of tooth pain receptors with those responsible for touch sensitivity will help define structural features unique to each type. Studies of developing, injured or inflamed teeth will help to understand the increased sensitivity associated with tooth maturation or with tissue damage. The response of sensory innervation to tissue healing will also be studied. Finally, analysis of sensory innervation in a variety of phylogenetic and functional types of teeth will help to understand the interactions between sensory receptors, pulp cells, dentin, enamel and specific tooth function. The following studies are proposed: Continued studies of the distribution of sensory receptors in teeth and their supporting tissues, of the ultrastructure of these receptors and of their interactions with associated cells. Electron microscopy, autoradiography, peroxidase cytochemistry, special stains, and immunohistochemical techniques will be used. Teeth of cats, rats, mice, rabbits and oppossum will be included, as well as extracted human teeth. Using rat and cat teeth, we will also study single dental receptors after functional identification; receptor location, ultrastructure and interaction with pulp cells in injured (drilled) teeth and during repair of injury; receptor structure and function in inflamed teeth; and cytochemistry of sensory receptors in normal or neurotoxin denervated teeth. The long-range objective of this work is to improve our understanding of basic cellular events underlying pain in order to improve treatment of pain.